Magnetic sensors using magnetoresistive devices capable of detecting the change of a rotation angle, etc. without contact are required to have good detection sensitivity to a rotating magnetic field. Used for high-sensitivity magnetoresistive devices is a spin-valve, giant-magnetoresistive (SVGMR) film comprising a pinned layer having magnetization anisotropy (simply called “pinned layer”), a non-magnetic intermediate layer formed on the pinned layer for cutting magnetic coupling, and a free layer formed on the non-magnetic intermediate layer and having a magnetization direction rotatable to an arbitrary direction by an external magnetic field. A Wheatstone bridge comprising devices each having the SVGMR film provides a magnetic sensor whose output voltage changes depending on the direction of an external magnetic field.
In a rotation angle sensor constituted by pluralities of SVGMR devices, the unevenness of the SVGMR device in magnetic properties such as an interlayer-coupling magnetic field Hint, an anisotropic magnetic field Hk, etc. increases an angle error (error of a rotation angle output from the rotation angle sensor). JP 2001-159542 A discloses a rotation angle sensor in which four devices cut out of the same wafer are connected to constitute a bridge. However, this rotation angle sensor fails to absorb unevenness in a wafer plane. The SVGMR device is sometimes referred to simply as “device.”
JP 2003-502876 A discloses a method for forming a device having pluralities of magnetic-sensing directions on the same wafer. In this method, after a desired pattern is formed, an external magnetic field is applied to the device while locally heating it by a heater, such that a pinned layer is magnetized in a desired direction. FIGS. 37 and 38 show the arrangement of devices obtained by this method. As shown in FIG. 38 with enlargement, there are devices whose pinned layers have antiparallel magnetization directions in an arrow direction 100, but there are no devices whose pinned layers have antiparallel magnetization directions in an arrow direction 100′ perpendicular to the arrow direction 100. Therefore, a bridge circuit with such device arrangement provides only an output having the same phase, failing to obtain a full-bridge output. Also, a device arrangement having an angle of 90° between devices cannot provide output signals with small angle error and distortion.
To suppress power consumption and heat generation to proper levels, the devices are preferably elongated to have higher resistance. However, the device with such a shape has non-negligible shape-induced anisotropy, exerting a large anisotropic magnetoresistance (AMR) effect generated from a free layer in the SVGMR film, resulting in increased angle error. JP 2005-024287 A proposes the connection of devices in a pattern in which their longitudinal directions are perpendicular to each other to cancel the AMR effect. Japanese Patent 3587678 proposes a semi-circular or spiral device pattern with reduced Hk. However, these structures only cancel the AMR effect or reduce Hk, but they fail to eliminate the unevenness of GMR characteristics to reduce angle error.